Fuel cells have been identified as a relatively clean and efficient source of electrical power. Alkaline fuel cells are of particular interest because they operate at relatively low temperatures, are efficient and suitable for operation in an industrial environment. Acid fuel cells and fuel cells employing other aqueous electrolytes are also of interest. Such fuel cells typically comprise an electrolyte chamber separated from a fuel gas chamber (containing a fuel gas, typically hydrogen) and a further gas chamber (containing an oxidant gas, usually air). The electrolyte chamber is separated from the gas chambers using electrodes. Typical electrodes for alkaline fuel cells comprise a conductive metal mesh, typically nickel, that provides mechanical strength to the electrode. Onto the metal mesh is deposited a catalyst which may for example contain activated carbon and a catalyst metal such as platinum. A single fuel cell does not produce a large voltage, and it is usually desirable to assemble a number of fuel cells into a stack to provide a larger electrical power output.
For some purposes it may be necessary to assemble a number of such stacks, to provide still greater electrical power output; and in this context there is a problem of providing the electrolyte to each of the stacks, and ensuring sufficiently uniform flow. If the electrodes are arranged in substantially horizontal planes in a stack and are fed from a common source there will be a significant pressure difference between electrolyte chambers at different heights in the stack. If the electrodes are arranged in substantially vertical planes in a stack, there will be a pressure difference between the top and bottom of each electrolyte chamber. For an aqueous electrolyte the pressure difference is about 15 mbar (1.5 kPa) over a height difference of 150 mm. In fuel cell, the electrical performance of the cell is sensitive to any such pressure variations, so the pressure variations within a cell stack and between different cell stacks should be minimised.